Now that The Big Bang Theory universe into 17 years of content. From its start in 2007 and Young Sheldon starting in 2017, it is all nearing an end. So. with 279 episodes over 12 years, there's bound to be some inconsistencies throughout the seasons.
From season 1 to season 12, all seven of the main characters have changed drastically, but some of their nuances just don’t match up with earlier episodes, and fans have certainly noticed these sudden changes in storyline. Whether small or big, these plot holes have definitely been spotted.
Penny’s Forgotten Sister
Penny throughout the seasons would drop hints of her family from time to time, whether that be about her brother who works in a meth lab, or her father who nicknamed her “slugger.” By the end of the show, she had been confirmed to have two parents, Wyatt and Susan, and a brother and sister, Randall and Lisa.
However, at her wedding, Lisa seems to be missing from the picture. There is no explanation as to why Lisa and her husband aren’t present at her sister’s wedding, along with all her other family , as fans noticed in season 10's, "The Conjugal Conjecture." The only explanation fans could come up with is that Lisa is doing jail time for accidentally shooting her husband … or the writers simply forgot about her.
Jimmy Speckerman & George Cooper Sr.
Sheldon has told stories of an unpleasant childhood, consisting of bullies and a not so great relationship with his father. All of which makes sense, until the spin off prequel: Young Sheldon. That’s because of Lance Barber, who was casted both as Sheldon’s childhood bully … and as his father.
In season 5, Lance Barber appears as Jimmy, Sheldon’s high school bully, who wants to reconnect. But in Young Sheldon, Lance Barber is cast as George Cooper Sr, a main role, where he plays Sheldon’s dad. Seems like the casting director forgot and now Sheldon’s bully is also his dad. Writer’s also changed his dad's characteristics in Young Sheldon, from a heavy alcoholic who cheats on his wife, to a caring husband who has a beer once in a while.
Sheldon Never Had A Spot At Work
Sheldon Cooper had many quirks and rules he abides to in his life, one of which is having an assigned seat in his apartment. He described it as the “single point of consistency.” It’s so important that it has been made a point since the pilot episode.
However this is not his only spot. He has a spot in Penny’s apartment, in a jail cell, in the Arctic and a chosen urinal at work. So why does he not have a spot at the cafeteria? An important set to the show, where the characters often hang out, seems to be the only place Sheldon forgets about liking a certain seat. He is more than comfortable changing seats, unlike any other time. His sudden comfort with change doesn’t match his personality.
Sheldon’s Cat Allergy
In the first season of the show, it is established that Sheldon is allergic to cats. This happens in season 1, where Leonard is down in the dumps over Penny’s new boyfriend. In his troubles, he mentions getting a cat, to which Sheldon refutes due to his asthma.
This ends up being a double plot hole, as in later seasons it is revealed that Leonard has asthma, not Sheldon. As for Sheldon’s supposed allergy to cats, in season 4's "The Zazzy Substitution," Sheldon adopts five cats. At no point does he find himself to be affected by Enrico Fermi, Richard Feynman, Edward Teller, Otto Frisch, and Zazzles. Either he lied about his allergy in season 1, or the writers forgot it.
Penny’s Surname & Dad’s Name
Penny’s family is rarely mentioned throughout the show, so much so that her full name is never mentioned. She is only referred to as Penny. So when she introduces facts about her family in early seasons, such as her dad, Bob, it was quick for fans to pick up on the name change.
Penny first mentions her dad in season 2's "The Maternal Capacitance." It’s here where she mentions Bob, her dad. But in season 4's "The Boyfriend Complexity," his name changes to Wyatt. Some fans had speculated that Penny’s surname was Wyatt, making the change a family nickname, but it was confirmed the writers never chose a surname for Penny. So it must have been a blunder on Bob/Wyatt’s name.
Raj Speaking Hindi
Rajesh Koothrappali was born in New Delhi, India where he grew up. He lived with his Indian parents and also went to school in India, before moving over to America later in life. So it would make sense for Raj to understand and speak Hindi, and he does.
In multiple episodes throughout the show he is shown to translate, talk or understand the Hindi language. In season 1, Raj speaks Hindi in his head, as he sings old lullabies his mother sang to him. In season 11, Raj translates Hindi heard in a cricket game. So why in season 10's "The Cognition Regeneration" does Raj tell Sheldon he never learnt Hindi, after Sheldon speaks to him in the language? It was a punchline that just doesn’t make sense.
Howard Studied At MIT For Six Years
It’s a running joke that Howard still lives with his mother for the early seasons. They show Howard and his mother are dependent on each other and have no intention of moving out. Howard often complains about this mother, and yet he’s spent his whole life at home with her. But he got a degree at MIT.
For Howard to get his degree, he would’ve had to study at MIT for six years … in Boston. However, he lives in Pasadena, on the other side of the country. But never in the show was it mentioned that Howard has moved out, nor could his mother even fathom the thought of him leaving the house, when he went to space for a few months.
The Broken Elevator
The yellow caution tape was a staple piece in the apartment building's stairwell. The elevator had been broken from the start of the show, with no hope of it being fixed until season 12. But the story behind the broken elevator isn’t revealed until season 3's "The Staircase Implementation."
It’s explained that it broke due to Leonard's science experiment gone wrong, causing an explosion that broke the elevator. However, in season 1, it’s mentioned the elevator has been broken for two years, making an incorrect timeline on when it broke. In later seasons, Howard tries to investigate the reason for the broken elevator, even though he was present when it broke. Each instance doesn’t match up with the original story of how the elevator broke, as if everyone has amnesia on the matter.
Bernadette’s Changed Attitude Towards Children
In the early days of Bernadette’s storyline, she explains to Howard that she doesn't get along well with children. This is after a birthday party where she snaps at the kids present. Howard says things will be different with their own children. But Bernadette reveals she never wants to have children.
However, in season 9, Bernadette discovers she’s pregnant, to which her only worry is how to tell Howard. She experiences no nervous or negative feelings about the pregnancy itself. In fact, she ends up having a second child in season 11 and in season 12, when Penny falls pregnant, with a fear of having kids Bernadette scolds her for not wanting them. Her mindset changed drastically, which probably happened due to Malissa’s real life pregnancy.
Amy’s Character Change
Amy was introduced in season 3's "The Lunar Excitation." Her personality was robotic and blunt. Howard described her as the female version of Sheldon. She had no need for romance or to follow normal social constructs like other girls do, making her a perfect candidate for Sheldon.
But as Amy became a main character of the show, the writers changed her. Suddenly she was animated, she had a care for female friends, romance and fashion. It is even revealed she tried to bleach her facial hair when she was young. Therefore indicating that Amy had always taken an interest in societal thoughts, boys and appearance, a version of Amy that certainly doesn’t match her initial introduction. The writer’s probably changed her to distinguish her as her own character instead of a water down version of Sheldon.